Revert "Revert "Use native async/await support in pub.""

sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart

Index: sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart b/sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart
deleted file mode 100644
index 537edc43635ba7e08a54910f10c412146d317735..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/lib/src/validator/executable.dart
+++ /dev/null
@@ -1,42 +0,0 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-library pub.validator.executable;
-
-import 'dart:async';
-
-import 'package:path/path.dart' as p;
-
-import '../entrypoint.dart';
-import '../validator.dart';
-
-/// Validates that a package's pubspec doesn't contain executables that
-/// reference non-existent scripts.
-class ExecutableValidator extends Validator {
-  ExecutableValidator(Entrypoint entrypoint)
-      : super(entrypoint);
-
-  Future validate() {
-    final completer0 = new Completer();
-    scheduleMicrotask(() {
-      try {
-        var binFiles =
-            entrypoint.root.listFiles(beneath: "bin", recursive: false).map(((path) {
-          return entrypoint.root.relative(path);
-        })).toList();
-        entrypoint.root.pubspec.executables.forEach(((executable, script) {
-          var scriptPath = p.join("bin", "$script.dart");
-          if (binFiles.contains(scriptPath)) return;
-          warnings.add(
-              'Your pubspec.yaml lists an executable "$executable" that '
-                  'points to a script "$scriptPath" that does not exist.');
-        }));
-        completer0.complete();
-      } catch (e, s) {
-        completer0.completeError(e, s);
-      }
-    });
-    return completer0.future;
-  }
-}